S04E06: 'Yellow Fever'

The Winchesters arrive in Colorado to investigate the suspicious deaths of three men who appear to have died of fright.

However, Dean inadvertently finds himself the next target after he becomes infected with the same mystery illness during a trip to the morgue.

Enlisting Bobby's help, Sam discovers that his brother is suffering from ghost sickness, an ancient disease that spirits inflict on people who use fear as a weapon. Victims are said to experience anxiety, then terror before being scared to death.

The Winchesters face a race against the clock as Dean is given only 24 hours to live unless they can track the buruburu ghost that infected him and reap some just desserts by literally scaring it to death.

Dean's irrational fears and over-the-top panic provide plenty of laughs, but this week's episode also has a darker side as he is forced to face his very rational fears of returning to hell and what Sam could become if he continues down his dangerous path with Ruby.